Recently, widespreading networks, such as a network (hereinafter called WAN (Wide Area Network)) typically represented by the Internet, which is publicly used over a wide area and a network (hereinafter called LAN (Local Area Network) which is installed in ordinary houses or the like and used locally, various data communications via these networks, are mainstream.
When image content, music content and the like are transmitted over a network, authentication and key exchange are performed for a communication partner and the content is enciphered and transmitted (refer to the following document).
DTCP Specification Volume 1 Version 1.3 (Information Version)
There arises herein the case that although copy and transmission in a home are permitted, content transmission to another home connected to WAN is restricted from the viewpoint of copyrights. For example, although a content of recorded television broadcast can be used if only it is used privately (in a home), if the content is transmitted via the Internet to a third party, it can be considered that this infringes the copyright, thus a restriction of this kind is therefore necessary.
Under this restriction, an apparatus (transmitter) for transmitting a content protected under copyright is required to judge whether a communication partner apparatus (receiver) for receiving the content is in the same LAN or connected via WAN (the Internet).
For example, whether the communication partner is connected via WAN (the Internet) can be known by checking from the IP address whether the communication partner is in the same subnet or by using the number (Hop Count) of IP routers through which an IP communication packet passes. However, if technologies such as VPN (Virtual Private Network) are used, even communications via WAN (the Internet) can establish a connection like the same subnet connected without an IP router. Namely, the content can be improperly acquired.